I cannot get a scene to render in blender
Your ParticleSystem2 setup for your pebbles is what is bogging down the render. It's currently set for 30k particles with 100x children to render which I think is the source of your infinite render time.

I would cut down on the number child particles by quite a bit. I would also use a blend texture from foreground to background to effect the particle density so it would give me more particles near the camera and less particles in the background. You may have to apply the curve modifier to get the blend texture to work properly.

You could also use a pebble texture for the background pebbles instead of actual geometry particles, which will cut down on your particle count as well.